1. Field of the Invention
The invention relates to a screening device for the wet screening of paper fiber suspensions. The device includes at least one screen plate provided with a plurality of screen openings, a support structure to which the screen plate is to be attached in a detachable manner with its back and a rotor that can be moved closely along the screen plate. An outlet opening is provided for the part of the paper fiber suspension passing through the screen openings.
2. Discussion of Background Information
Screening devices are used in paper stock preparation, e.g., in sorters and pulpers of the pulp and paper industry, in order to treat the fiber suspension during a wet screening. In most cases, non-fibrous impurities and not yet disintegrated paper are thereby to be retained at a screen as a result of their size and then to be discharged. The passing of fiber suspension through the screen openings involves a considerable loss of pressure. This leads to strong forces pressing against the screen, which are absorbed as compressive forces by the support structure. The screens of such devices are usually made of metal, e.g., alloyed high-grade steel.
In order to prevent a clogging of the screen openings, typically scrapers attached to a rotor are used, which move closely along the openings, thereby creating hydraulic pressure impulses and hydraulic suction impulses. These impulses can cause the screen plate to vibrate, which stresses both the support structure and the screen plate. Other hydraulic impulses (thrusts) that can endanger said components originate in the periphery of a screening device, e.g., actuated sliders and pumps in the connecting lines. Even welded components are endangered by the vibrations.
The mentioned stress conditions during wet screening necessitate a complex and sturdy attachment of the screen plates, which implements in most cases a reduction of free screen area.
It is known that the effect of the scrapers can be improved by protruding strips, as these cause turbulences that prevent solid materials from depositing. Mounted strips of this type are disclosed, e.g., in DE 195 06 084A1.